For years, most of us have envisioned climate change as a long-term problem that requires a long-term solution. But as the years pass—and with the calendar soon to flip over to 2013—without any substantial attempts to cut greenhouse gas emissions worldwide, this impression needs to change in a hurry.

According to a new paper published today in the journal Nature Climate Change, there’s a startlingly small number we need to keep in mind when dealing with climate change: 8. That’s as in 8 more years until 2020, a crucial deadline for reducing global carbon emissions if we intend to limit warming to 2°C, according to a team of researchers from a trio of research institutions—the International Institute for Applied Systems Analysis and ETH Zurich in Switzerland, along with the National Center for Atmospheric Research in Boulder, Colorado—who authored the paper.

They came to the finding by looking at a range of different scenarios for emissions levels in 2020 and projecting outward how much warming each one would cause for the planet as a whole by the year 2100. They found that in order to have a good chance at holding long-term warming to an average of 2°C worldwide—a figure often cited as the maximum we can tolerate without catastrophic impacts—annual emissions of carbon dioxide (or equivalent greenhouse gas) in 2020 can be no higher than 41 to 47 gigatons worldwide.

That’s a problem when you consider the fact that we’re currently emitting 50 gigatons annually; if present trends continue, that number will rise to 55 gigatons by 2020. In other words, unless we want catastrophic levels of warming, we need to do something, quickly.

The researchers also weighed a number of technological approaches that could help us bring this figure down by 2020: mass conversion to nuclear power generation, rapid adoption of energy-efficient appliances and buildings, electric vehicle usage and other means of reducing fossil fuel use. “We wanted to know what needs to be done by 2020 in order to be able to keep global warming below two degrees Celsius for the entire twenty-first century,” said Joeri Rogelj, the lead author of the paper, in a statement.

It turns out that some combination of all of these methods will be necessary. But lowering global energy demand—in large part, by increasing efficiency—is by far the easiest route to making a dent in emissions soon enough to hit the goal by 2020.

If the reduction target isn’t reached by 2020, avoiding catastrophic warming could theoretically still be possible, the researchers note, but the cost of doing so would only increase, and our options would narrow. If we start cutting emissions now, for example, we might be able to hit the goal without increasing nuclear power generation, but wait too long and it becomes a necessity.

Waiting past 2020 would also require more costly changes. In that case, “you would need to shut down a coal power plant each week for ten years if you still wanted to reach the two-degree Celsius target,” said Keywan Riahi, one of the co-authors. Waiting would also make us more reliant on as-yet unproven technologies, such as carbon capture and storage and the efficient conversion of crops into biofuels.

“Fundamentally, it’s a question of how much society is willing to risk,” said David McCollum, another co-author. “It’s certainly easier for us to push the climate problem off for a little while longer, but…continuing to pump high levels of emissions into the atmosphere over the next decade only increases the risk that we will overshoot the two-degree target.”